The present invention relates to electric welding assemblies having multiple weld gun arms for producing multiple simultaneous welds in a single pass. In particular, the present invention relates to assemblies where one arm of a multiple arm weld gun is retractable.
Resistance welding utilizes the flow of electricity to permanently join two or more overlapping metallic work pieces to one another. Typically, the metallic work pieces are placed between two opposing electrode tips, which are on the jaws of a weld gun arm. The electrodes are then forced together until their tips contact the outer surfaces of the work pieces at a pressure sufficient to sandwich the work pieces and ensure an adequate electrical contact between the electrode tips and the work pieces. An electrical current is induced to flow from one electrode tip to the other electrode tip by way of the sandwiched work pieces. The work pieces act as conductors in the resulting electrical circuit, and resistance to the flow of electrical current at the interfaces between the metals generates heat. The affected metal of each work pieces selectively becomes molten, and interacts with molten metal of an adjacent work pieces to form a weld nugget that permanently bonds the work pieces together at the point of electrode tip contact.
A number of factors relate to the creation of a weld nugget, including the force and area of contact between the electrode tips and the work pieces, the level of current flow, the length of time the current flow lasts, degree of work pieces imperfection, and even the condition of the electrode tips themselves.
Weld guns used in manufacturing processes typically are required to make multiple consecutive welds on a given work pieces. In such a situation, devices exist for moving the work pieces between individual welds, moving the weld gun between individual welds, or both. For example, the electric welding gun may cycle through various locations, i.e. between an operational position with a work pieces and a resting position. The work pieces may be placed on a moving platform that manipulates the work pieces for a welding operation with a movable weld gun. After the work pieces is manipulated, the weld gun may move toward the work pieces to perform a weld cycle, after which the weld gun moves away from the work pieces to allow movement of the piece and manipulation of the next piece to be welded. In some applications, the weld gun must make a significant number of consecutive welds before further manipulation of the work pieces. In such applications, the amount of time required to move the weld gun to make the consecutive welds becomes a rate limiting step.
It is known to mount multiple weld gun arms to a single weld gun to decrease the amount of time required to make a significant number of consecutive welds. For example, simply adding one additional gun arm to a weld gun such that both arms are capable of simultaneous welding operation cuts the time required for performing a series of multiple consecutive welds nearly in half. Multiple arm weld guns, usually in the form of dual arm weld guns, have the advantage of being able to make several welds at one time, which decreases the cycle period of the weld gun assembly. In current multiple arm weld gun systems, artificial intelligence controls the weld gun arm position process during a weld cycle by first operationally orienting the multiple arm weld gun to the work pieces. The process includes creating welds by closing electrode tips of the weld guns about the work pieces, creating welds, reorienting the multiple arm weld gun with respect to the work pieces, and creating additional welds. Multiple arm weld guns are thus able to complete more than one weld at once, depending upon the number of weld arms on the weld gun, thereby shortening the period of time it takes to complete all the welds on a work pieces. As a result, the weld cycle period is shortened, i.e. the period of time from the beginning of one work pieces to the beginning of the next work pieces is decreased.
However, conventional multiple arm weld guns have a significant disadvantage due to their increased size over single arm assemblies, which are required to accommodate multiple arms on a weld gun. Specifically, currently known multiple arm weld guns are not suitable for welding many types of work pieces, because the multiple arm weld gun cannot make welds in spatially restricted locations of mated work pieces if the weld gun has difficulty gaining access to the work pieces where the weld is required.
One solution to the problem of the too-large-multiple arm-weld-gun is to use a second, single arm weld gun that can be accommodated in the spatially restricted space. However, this provides unsatisfactory results because of the added inefficiencies of using two weld guns. The purpose of multiple arm weld guns is to reduce the number of required weld guns, not to increase the number. The added, single arm weld gun would be similarly expensive to design, maintain, and operate as the multiple arm weld gun. In addition, the introduction of a second separate weld gun would unduly increase the cycle period because one weld gun would have to be moved out of the way in order of the other weld gun to move into its welding position.
Accordingly, there is a need to provide an improved electric welding system that minimizes or eliminates one or more the problems set forth above.
A multiple arm weld gun is provided wherein one or more weld gun arms on the multiple arm weld gun are able to retract away from a work pieces while at least one other arm remains operational, thus allowing a multiple arm weld gun to act as a single arm weld gun. As a result, once one or more weld gun arms are retracted, the remaining weld gun arms may be repositioned with respect to the work pieces in a space not previously accessible to the multiple arm weld gun before retraction of an arm. While all weld gun arms may be retractable, preferably only at least one arm is not retractable. The ability to retract all but one of the weld gun arms effectively overcomes the problem of multiple arm weld guns that are too large, without requiring the use of a separate single arm weld gun.